Catalytic converters are an exhaust emission control device fitted to vehicles that convert toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a reaction.

Source: https://www.doncasterfreepress.co.uk/news/crime/driver-loses-two-catalytic-converters-in-six-weeks-after-ps3600-theft-at-doncaster-park-and-ride-4091300

Catalytic converters are fitted to vehicles to reduce the amount of pollution emitted from cars, but they are also a target for thieves who harvest the components from cars before selling them on the black market.

Source: https://www.gazette-news.co.uk/news/23225363.essex-catalytic-converter-thefts-topped-500-last-year/?ref=rss